Department of Homeland Security Secretary Kirstjen Nielsen leaving administration

On Friday, the White House announced it was withdrawing the nomination of Ronald Vitiello to lead Immigration and Customs Enforcement (ICE). As they toured a section of newly rebuilt barriers, Nielsen was at Trump's side, introducing him to local officials. She returned to Washington afterward on a Coast Guard Gulfstream, as Trump continued on a fundraising trip to California and Nevada.

The administration was forced to rescind the practice after massive public uproar, but Nielsen always maintained she did not oversee a family separation policy, but rather one of increased prosecution of migrant parents crossing the border illegally.

The people were not authorised to speak publicly about internal matters and spoke to The AP on condition of anonymity. Trump threatened to fire her and she previously considered resigning, but officials at the time recognised there were no obvious successors in place.

As recently as last week, Nielsen was busily announcing plans to reassign hundreds of Customs and Border Protection agents to the southern border to "address the influx of migrants" in certain areas.

After the resignation of Homeland Security Secretary Kirstjen Nielsen, chief political correspondent for the Washington Examiner Byron York, a Fox News contributor, warned the migrant situation has "clearly reached the breaking point". In a letter provided Sunday night by her office, she said the resignation was effective immediately, though hours later she agreed to stay through Wednesday to ease the transition. She thanked Trump and DHS staff for their hard work.

Repeatedly subjected to tough questioning by Democrats at congressional hearings, Nielsen became a lightning rod for criticism of Trump's policies. Immigration was arguably the most important issue in his 2016 campaign.

Nielsen was also responsible for the sprawling internment camps to hold refugees and the "metering" system and "remain in Mexico" policies meant to make life hell for people seeking legal asylum. Despite Trump's crackdown at the southern border, the president has voiced frustration over the high levels of illegal immigration. The Wall Street Journal reported in November that Trump had made a decision to replace Ms Nielsen. Her departure provides political fodder but little comfort, given Trump's demands for ever more severe policies.

She wasn't intent on quitting but was prepared to, sources tell us. In November, leaks from the White House suggested she would be out by the end of the year as Trump fulminated against what he complained was her weak performance.

Trump insists that the arrival of immigrants across the southern USA border constitutes a national emergency so important that he sidestepped Congress' refusal to provide him with billions of dollars he requested to build the border wall.

Commenting on her tenure, the ACLU tweeted Sunday: "From the family separation crisis she created and defended, to restricting immigrants' rights to seek asylum, to relentless and pointless efforts to build Trump's border wall, Nielsen's department served as the key to Trump's unconstitutional and anti-immigrant agenda of fear".